1. Field of the Invention
The present invention relates to plastic containers for medical fluids such as intravenous solutions and blood, and more particularly, to a fabricated film container having a novel film material.
2. Prior Art
A number of film materials are known for use in medical fluid containers. A widely used material in the past has been polyvinyl chloride, which is used at the present time in blood bags and in commercially available flexible intravenous solution containers. Polyvinyl chloride, however, is disadvantageous in that it is often formulated so as to be brittle at low temperatures and to contain plasticizers which may be extracted by certain intravenous solutions.
Several polyolefins are also known for application in the field of medical containers, particularly in semi-rigid containers, with rigid shoulder and/or base portions, which assume a free-standing shape and collapse upon withdrawal of the container's contents. This design eliminates the need for an air inlet in such containers, an important advantage of flexible medical fluid containers generally. See for example, U.S. Pat. No. 3,921,630, which discloses a propylene-ethylene copolymer and U.S. Pat. No. 4,100,953, which suggests that medium and high density polyethylene may be used for such containers. In fact, at the present, most semi-rigid containers are currently made from propylene/ethylene copolymers. U.S. Pat. No. 4,140,162 suggests various propylene/styrene-ethylene-butylene-styrene (SEBS) blends for a blow-molded oval container with more flexibility. It is often desirable, however, that the container be in a flexible bag form to enable flat shipment of empty containers and more convenient storage.
Another type of medical fluid container, known to be used outside the United States, is a flexible laminate container, such as described in U.K. No. 2,040,263A. This film bag comprises a three layer laminate consisting of a propylene outer layer, a polyamide middle layer, and an ethylene/butylene inner layer. U.S. Pat. No. 4,210,686 discloses a polyolefin/SEBS blend as one layer of a laminate, with a polyolefin outer layer. The polyolefins are derived from propylene, ethylene, and 4-methylpentene-1. The laminate approach generally employs a rubbery material for softness and a high temperature material such as polypropylene or high- or medium-density polyethylene to permit very high temperature resistance during sterilization. A drawback to the laminate approach, however, is that scrap materials from the manufacture of such films cannot be reground into feedstock for the film-making equipment.
Prior art sterilization plastic containers have heretofore been constructed of film or flexible materials having a crystalline melting point (MP) in the range of 130.degree. to 165.degree. C. in order that they may be heat sterilized without intolerable distortion. Thus, polypropylene, with copolymers or blends, with MP's in the range 165.degree. C. have been commonly used. They have been described for use with SEBS having a melting point around 120.degree. C. On the other hand, polyethylenes (MP 109.degree. C. to 125.degree. C.) have been used in small amounts, if at all, as softening agents. Polypropylene, however, is undesirable in that it may not be irradiated as, for instance, in radiation sterilization and in that it becomes brittle at low temperatures (around 0.degree. C.) and in that it is inherently stiff, and will spring back to its molded shape.
It is therefore among the objects of the present invention to provide a medical fluid container which has a flexible film body for flat storage and collapse, together with good low temperature flexibility in the film body, sufficient temperature resistance to softening and/or melting during steam sterilization, and capability for radiation sterilization. Other objects of the present invention, which will become apparent from the following description include providing a container of film material which has superior optical clarity and a combination of flexibility and strength which impart superior handling characteristics over a wide temperature range.